If you want the background image to cover the entire element, you can set the background-size property to cover.
Also, to make sure the entire element is always covered, set the background-attachment property to fixed:
This way, the background image will cover the entire element, with no stretching (the image will keep its original proportions):
<style>
body {
background-image: url('cat.jpg');
background-repeat: no-repeat;
background-attachment: fixed;
background-size: cover;
}
</style>
Live Demo & Try it yourself!